Windshield cleaner



April 15, 1958 M. BITZER 2, 0, 1

WINDSHIELD CLEANER Filed Aug. 31, 1954 3 Sheets-Sheet 2 IN V EN TOR.

BY Martin Bi izer C214, M,M*@M

April 15, 1958 .M. BITZER 2mm WINDSHIELD CLEANER Filed Aug. 31, 1954 3Sheets-Sheet 3 IN V EN TOR.

Martin Bizzer WINDSHIELD CLEANER Martin Bitzer, Kenmore, N. Y., assignorto Trico Products Corporation, Bulfalo, N. Y.

Application August 31, 1954, Serial No. 453,215

16 Claims. (Cl. 15-253 This invention relates to a Windshield cleanerfor automotive vehicles, and more particularly to a cleaner adapted toeliminate the blind spot existent on the central portion of Windshieldsduring heavy Weather.

Heretofore, windshield cleaners have comprised two blades, one locatedsubstantially in front of the operator of the vehicle and the othersubstantially in front of the passenger, with both blades oscillatingabout pivots located proximate to the lower molding of the windshield.in some systems the blades were run in parallelism While in others theyran in opposition or clapped hands relationship. However, regardless ofthe relative motion between the blades, the central portion of thewindshield was beyond the wiping area of either blade, and thus remainedcompletely obliterated in heavy weather, obstructing the vision of theoperator.

With the increased employment of motor vehicles and the tratliccongestion resulting therefrom, the need for greater visibility is ofparamount importance and has resulted in the design of vehicles withever increasing glass area. But, in heavy weather when the need formaximum visibility is most important, the increased glass area is of nosignificance whatsoever if such area remains obliterated. There istherefore a distinct need for a cleaning system which is adapted toclear of precipitation substantiaiiy the entire windshield. Accordingly,it has been proposed that the Squeegees be mounted so as to wipeoverlapping areas. However, in order to accomplish this without havingthe Squeegees interfere with one another it is necessary that they runin parallelism. Such relationship presents a problem when the blades areparked. If operated in parallelism at all times, one of the blades mustnecessarily be parked at substantially the center of the shield, aposition in which it will unavoidable obstruct vision.

In accordance with the present invention, the wipers run in synchronizedmovement and park in out-of-phase position. In the illustratedembodiments, there is utilized a connecting rod motor, or a parkingmotor, with the motor cylinder and piston built into the connecting rodwhich transmits the movement from the wiper motor to a auxiliary wipershaft.

The control valve for this system is arranged so that in its runningposition there is a differential pressure applied to the opposite sidesof the piston in the connecting rod motor in the direction to push thepiston out as far as built-in stops will permit it to go, therebyincreasing the length. The differential pressure is held continuously inthis connecting rod motor during Wiper operation so that the entiremechanism functions as a solid connecting rod without relative movementof any of its parts. In this position the length of the connecting rodis such that the arms operate in parallel positions, and this conditionobtains as long as the Wiper is running either at full speed or any ofits reduced speeds of operation. When the control valve is moved to theoff position, dilferential pressure is cut oif entirely from the runningmotor, and from both sides of the connecting rod'motor, therebyarresting the United States Patent mechanism in whatever position it isat the time when the valve is so moved. After this, the valve is thenmoved farther in the direction of the oil position to again set up apressure 'ditferential in the connecting rod. motor, but in a reversedirection. This reversal of pressure on the piston in the connecting rodmotor will now move the piston into the cylinder and shorten theconnecting rod to a predetermined value that is controlled by stops inthe cylinder to limit the motion of the piston. During this operationthe wiper which moves the easier will first go to its parked position,and the further movement of the connecting rod piston relative to itscylinder will effect a similar movement of the other wiper unit to itsparked position. This control valve position for the parking ispreferably one that has to be held manually against a.

recovery spring, the control valve will immediately revert to its offposition as soon as the control valve is released by the operator of theautomobile, and this will relieve all parts of the system from anypressure differential, as indicated at the outset of this description.Obviously, the arrangement would work without blade interference duringthe running, and it should be equally obvious that this arrangementwould work without blade interference during the parking. The systemwill start without blade interference as soon as the motor is turned onto provide a reversal of pressure on the connecting rod motor which willaccelerate the motion of the blade on the passenger side to get it outof the way of the companion blade.

Accordingly, it is the primary object of the present invention toprovide a windshield cleaning system which is adapted to clean theheretofore obliterated central portion of the shield as well as thoseareas previously cleaned, Without having the blades interfere with oneanother in operation and yet being capable of parking substantially outof the field of vision of the operator of the vehicle.

For a greater appreciation of this and other objects of the inventon,reference is made to the following specifications and accompanyingdrawings wherein:

Fig. 1 is a fragmentary perspective view of an automotive vehicleequipped with a windshield cleaning system constructed in accordancewith the instant invention;

Fig. 2 is a longitudinal sectional view of the pneumatic link;

Fig. 3 is a sectional view of the master control valve taken on lineIII-III of Fig. 4;

Fig. 4 is an end view of the rotary control valve;

Fig. 5 is a sectional view of the adjustable flow control valve taken online V-V of Fig. 4;

Fig. 6 is an end view of the master control valve with the cover plateand shaft assembly removed;

Fig. 7 is an exploded view of the valve element an valve plate; I i

Fig. 8 is a perspective View of the drive lever;

Figs. 9, 10 and 11 are schematic flow diagrams illustrating the cycle ofoperation of the present invention; and

Fig. 12 is a diagrammatic view of a modified form of the invention.

Referring now more particularly to the drawings, the numeral 1 generallydesignates an automotive vehicle having a windshield 2 and wipers 3 and4. The wipers are mounted on parallelogram arms 5 and 6 of conventionaldesign which maintain the wipers in a substantially vertical positionthroughout their operating arcs. Motor 7 which is of thesuperatmospheric type such as that disclosed in United States LettersPatent No. 2,632,196, is mounted on the firewall of the vehicle and hascrank arm 8 fixedly attached to its drive shaft 9. The outer end of thecrank arm is connected to a multiple element transmission lll whichincludes a pneumatic link 11. The

motion of the drive shaft is transmitted to wiper 3 via thetransmission, crank arm 12, rockshaft 13 and paral- Patented Apr. 15,1958 lelogram. arm 5. Parallelogram arm 6 derives its motion directlyfrom drive shaft 9.

The master control valve 14 may be located at any position within thepassenger compartment convenient to the. operator of the vehicle-Protruding from the rear of the valve housing are four nipples 1'5, 16,17 and 18 as best seen in Figs. 3 and 4. Hose 19, shown fragmentarily inFig. 1 interconnects nipple 16 and a source of superatmosphericpressure, not shown. Hose 20 interconnects nipple with the parkingcylinder of motor 7, while hose 21 Td. oif hose 20, interconnects theleft side of the pneumatic link with nipple 15. Hose 22 runs from nipple18 to the right side of the pneumatic link while hose 23 interconnectsnipple 17 with the left side of motor 7.

Referring now more particularly to Figs. 3 and 4, it may be seen thatthe master control valve comprises a circularcasing 24 from which thefour equally spaced nipples protrude, and a substantially conical coverplate 25. Shaft 26 having'a sealing ring 27 is passed through a centralopening in the cover plate. Torsion spring 28 carried on a centralportion of the shaft is maintained in a prestressed condition by havingone of its ends anchored in a slot provided therefor in the shaft, andhaving its opposite end abutting tongue 29 of drive lever 30. The leveris maintained in driving engagement with the shaft by means of flats onthe latter engaging a substantially rectangular aperture in the lever.As a result, spring 28 is normally maintained in its prestressedcondition regardless of the manner in which the shaft may be rotatedsince the lever will at all times rotate with the shaft.

Valve element 31 which may be composed of rubber or some similarmaterial is maintained in. driving engagement with valve plate 32 bymeans of 'a plurality of bosses 33, 34 and 35 on the element engagingmating holes 36, 37 and 38 on the plate. Conical spring 39 carriedon theextreme end of the shaft 26 insures close contact between the elementand plate and also between the element and the face of casing 24.

The flow of air into the system is controlled by means of valve 40 bestseen in Fig. 5. Air flowing from the source enters nipple 16, passesfilter screen 41 and enters flow chamber 42 through orifice 43. Sealingring 44 prevents the leakage of air past needle valve 45, while theconical tip of the needle valve in conjunction with orifice 46 controlsthe rate at 'which the air will flow into passageway 47. From passageway47 the air flows drilled in the casing 15. Similarly, air from the rightside of pneumatic link 11 flows to the atmosphere via hose 22, orifice55 of nipple 18, groove 61 and orifice 64 of torsion spring 28 isbrought into substantial en- 'link 11 so as to urge piston 69 to theleft.

gagement with abutment 65 of casing when the shaft 26 is rotated tobring the valve to the off" position.

Further rotation increases the strain on torsion spring 28 since itsinturned end 64 is prevented from rotating with the remainder of thespring because of engagement with abutment 65. If such rotation iscontinued until shoulder 66 of valve plate 32 strikes abutment 68 ofcasing 15, the master control is placed in the park position illustratedin Fig. 10. High pressure air from hose 6 19 enters the dome in theusual manner via nipple 16, passageway 47 and orifice 48. From the domethe air passes through orifice 50 and its associated groove in element31 and into hose 22 via orifice 55 in nipple 18. From hose 22 the airenters the right side of pneumatic Concurrently, air leaves the leftside of the pneumatic link via hose 21 and joins the air leaving theright side of motor 7 at hose 20. The air in hose 20 evacuates to theatmosphere via orifice 56in nipple 15, groove 60 in the valve elementand Y orifice 62 in the casing. Similarly, the air from the throughorifice 48 and via slot 49 in shaft 26 into the I dome formed by theconical cover plate. prevents the air from flowing out past the shaft,and it enters the desired nipple or nipples viamating 110158505 51, 52and 53 of the plate'32 and element 31. Which, if any, of the nipples theair will enter is determined by whether or not the holes in the plateand element are in registration with holes 54, 55 and 56 of nipples 15,17 and 18 respectively. 1

Referring now more particularly to Figs. 9, 10 and 11, when the mastercontrolis turned to the position indicated in Fig. 9, the entire systemis neutralized, air flowing into the master control enters the dome asdescribed above. However, since neither orifice nor orifice 51 of thevalve element 31 is in registration with any of orifices 54, and 56, thehigh pressure air cannot enter the system. Pressure builds up in thedome until a point is reached where the air ceases to flow. Air in theleft side of pneumatic link 11 flows out through hose 21 to hose 20where it is joined by air flowing out of the right side of motor 7. Hose20 empties into nipple 15, orifice 56 of which is in register withgroove 60 of the valve element 31. The air then passes to the atmospherevia orifice 62 of the valve casing 15. Air from the left side of motor 7passes out through hose 23 and enters orifice 54 of nipple 17. Fromorifice 54 the air flows along groove 61 and empties into theatmosphere. via orifice 63 Sealing ring 27 left side of the motor isevacuated via hose 23 so as to neutralize any pressure differentialwhich might exist across piston of the drive motor. The air in hose 23flows to orifice 54 of nipple 17 and then to the atmosphere via groove61 and orifice 63. It should be remembered that when shaft 26 is rotatedto place the master control in the par position, spring 28 is stressedby the engagement of inturned end 64 with abutment 65. It is thereforenecessary to manually hold the valve in the par position until squeegees3 and 4 reach the position indicated in solid in Fig. 1. When the shaftis released it' automatically returns to the off position of Fig. 9.With the master control in this position the high pressure air isevacuated to the atmosphere as described above and the entire system isneutralized.

Referring now more particularly to Figs. 1 and 2, the pneumatic linkcomprises a cylindrical casing 71 enclosing the piston 69. Hoses 21 and22 are coupled to pressure fittings 21a and 22a respectively. Piston rod72 is rigidly afiixed to the piston and extends out of the cylinderwhere it is attached to connecting rod 73, the opposite end of whichv ispin connected to crank arm 8. Connecting rod 74 is connecting to crankarm 12 at one end and to the pneumatic link at its opposite end.

With the master control in the o position and the system neutralized, nopressure differential exists across either piston 69 of the pneumaticlink or piston 70 of the motor. Rotation of the mastercontrol to thepark position of Fig. 10 causes high pressure air to flow into the rightside of the pneumatic link and move piston 69 to the left so as tocontract the transmission 10. Such contraction compels the system toassume the parked position indicated in solid in Fig. 1. After theblades are parked, the operator releases the master control which willunder the urging of spring 28 return to the off position of Fig. 9 so asto release the pressure on the right side of piston 69. The system will,due to inertia and friction, remain in the parked position untilactivated.

When it is desired to activate the system, the master control is turnedto the run" position of Fig. 11. In this position, shoulder 67 of valveplate 32 is adjacent to abutment 68 of casing 15. The abut-ment acts asa positive stop to prevent the inadvertent rotation of the valve elementbeyond the run position. Air enters the dome in the usual manner andflows into hose 23 via orifices 51 and 54 which are in registration witheach other.

amt-n4 ,-taneously air enters hose 20 via orifices 50 and 56 and theintervening groove in the valve element. From hose 20 the air flows intothe parking cylinder of the motor and also into the left side of thepneumatic link via hose 21. The high pressure air forces piston 69 tothe right so as to expand transmission 10 as shown in phantom in Fig. l.operate in phase i. e. they will both move to the right With thetransmission expanded the wipers will and then to the left at the sametime. The operating arcs are so designed that the extreme rightwardtravel of squeegee 3 overlaps the extreme leftward travel of squeegee 4so as to eliminate the heretofore existent blind spot at the center ofthe shield. In addition it should be noted that the transmission ismaintained solid in its expanded position by the application of:pressure to the left side of piston 69 for so long as the mastercontrol is in the run position. When it is desired to deactivate thesystem the master control is to tated through off to park so as tocontract the transmission and then automatically returned to off by thetorsion spring to relieve the pressure as described above.

Thus, when the system is actuated, the transmission parts 74, 11 and 73function in the manner of a solid connecting rod transmitting drivingforce from crank arm 8 to crank arm 12, and there is no relativemovement between casing '71 and piston 69 of the expansible pneumaticlink 11. Link 11 therefore is mounted to reciprocate as part of thetransmission, and conduit-s 21 and 22 are sufficiently flexible tofollow the moving link 11.

Referring now more particularly to Fig. 12 wherein a modified form ofthe invention is shown. Herein 1a pneumatic motor 7 which may be ofeither the superatmospheric or vacuum type is employed in conjunctionwith a dummy motor 80. The dummy motor contains no valving, and the twosides of its pressure chamber are connected to the corresponding sidesof motor 7 by conduits 81 and 82. This insures the duplication in motor80 of the pressure conditions existent in motor 7. The Squeegees 3 and4' are of conventional design and are mounted on oscillatable arms and 6which drivingly engage shafts 13' and 14' of the motors 7' and 80.Because of the identity of pressure conditions within the two motors,the wipers will normally oscillate in phase with one another. The mastercontrol and pneumatic system will operate in a manner substantiallyidentical to that disclosed above relative to the species of Fig. 1. Thesystem will be neutralized when the control is in the off position, thetransmission will contract so as to park the blades out of phase whenthe control is turned to the park position and the transmission willexpand so as to compel the wipers to operate in phase when the controlis turned to the run position, all as described above.

In this parking action, the motor that moves the easier of the two willrespond first to the pressure, and as soon as it reaches its parkingposition, the further contraction in the transmission will now compelthe other motor unit to move to its parking position, thereby bringingboth blades to their fully parked positions at the completion of thecontraction in the transmission. From this and a similar action thattakes place in the system with one motor when the simultaneous controlfor motor and expanding or contracting transmission is operated, it willbe observed that this expansible and contractible element in thetransmission actually becomes another motor during the first movementswhen the wiper is turned on and again during the parking when the systemis deactivated. Therefore, the transmission constitutes a connecting rodmotor or parking motor for extending and contracting the pneumatic linkthat joins the wipers.

contractible and expansible transmission element will be working betweena single blade unit and a two blade unit, therefore, it is obvious thatin the parking operation the single blade unit will move first therebybringin'g'this one blade out of parallel synchronism into its oppositeposi tion ahead of the parking movement that is subsequently given tothe two blade unit. Thus it will be seen that the blade that lays downinto contact with the cowl of the windshield will get there firstwithout interference from the other blade which will subsequently comedown on top of it.

It may therefore be seen that by employing the present invention it ispossible to eliminate blind spots on the windshield by operating theblades in phase so that their wiping arcs overlap without anypossibility of blade interference. Additionally, and by the simplerotation of a control valve the blades are thrown out of phase to permitparking out of the line of vision.

Having thus disclosed exemplary embodiments thereof, what I claim as myinvention is:

1. A windshield cleaning system for automotive vehicles comprising, aplurality of blades adapted to clear an associated windshield ofmoisture, motive means for driving said blades to and fro across thewindshield, a transmission including an expansible link operativelyconnected to said blades and operable to hold said blades for operatingin phase or to park said blades out of phase,

and means for controlling the contracting and expanding of said link. I

2. A windshield cleaning system for automotive vehicles comprising, aplurality of blades adapted to clear an associated windshield ofmoisture, motive means for driving said blades to and fro across thewindshield, an expansible and contracti'ble pneumatic link operativelyconnecting said blades, the phase relationship of said blades beingdetermined by Whether or not said link is being maintained in anexpanded or contracted condition, a pneumatic system for expanding andcontracting said link, and means for controlling the pneumatic system.

3. A windshield cleaning system for automotive vehicles comprising, aplurality of blades adapted to clear an associated windshield ofmoisture, motive means for driving said blades to and fro across thewindshield, the inboard ends of the operating strokes of said'bladesoverlapping one another, an expansible link operatively connected tosaid blades, the phase relationship of said blades being determined bywhether or not said link is being maintained in an expanded orcontracted condition, and means for controlling the contracting andexpanding of said link.

4. A windshield cleaning system for automotive vehicles comprising, aplurality of blades adapted to clear an associated windshield ofmoisture, motive means for driving said blades to and fro across thewindshield, the inboard ends of the operating strokes of said bladesoverlapping one another, a transmission including an expansiblepneumatic link operatively connected to said blades, the phaserelationship of said blades being determined by whether or not said linkis being maintained in an expanded or contracted condition, a pneumaticsystem for expanding and contracting said link, and means for cotrollingthe pneumatic system.

S. A windshield cleaning system for automotive vehicles comprising, aplurality of blades adapted to clear an associated windshield ofmoisture, motive means for driving said blades to and fro across thewindshield, a transmission including an expansible link operativelyconnected to said blades, the phase relationship of said blades beingdetermined by whether or not said link is being maintained in anexpanded or contracted condition, and control means, said last namedmeans being adapted to simultaneously control the activation and de-2,&30,3.14-

activation. of the motive-means as well-as the expansion and contractionof the'expansible link.

6. A-windshield cleaningsystem for automotive 1 cles comprising aplurality of blades-adapted to clear an associated windshield ofmoisture, motive means, for driving said blades to andfro across thewindshield, a transmission including an expansiblepneumatic link oneratively connected to said blades, the phase relationship of saidblades being determined by whether or not said link is being maintainedin. an expanded or contracted condition, a pneumatic system forexpanding and contracting said link, and control means, said last namedmeans being adapted to simultaneously control the activation anddeactivation of' the motive means as well as the expansionandcontraction of the expansible link.

7. A Windshield cleaning system for automotive vehiclescomprising, aplurality of blades adapted to clear an associated windshield ofmoisture, motive means for driving said blades to and fro across thewindshield, the inboard ends. of the operating strokes of said bladesoverlapping one another, ;a transmission including an expansible linkoperatively connected to said blades, the phase relationship of saidblades being determined by whether or notsaid :link is being maintainedin an expanded or contracted condition, and control means, said lastnamed means being adapted to simultaneously control the activation anddeactivation of the motive means as well as the expansion andcontraction of the expansible link.

8. A windshield cleaning system for automotive vehicles comprising, aplurality of blades adapted to clear an associated windshield ofmoisture, motive means for driving said blades to and fro across thewindshield, the inboard ends of the operating strokes of said bladesoverlapping one another, an expansible pneumatic link operativelyconnecting said blades for operating in unison and to park out of phase,a pneumatic system for expanding and contracting said link and controlmeans, said last named means being adapted to. simultaneously controlthe activation and deactivation of the motive means as well as theexpansion and contraction of the expansible link.

9. A windshield cleaning system for automotive vehicles comprising, aplurality of blades adapted to clear an associated windshield ofmoisture, a first motor for driving at least one of said blades to andfro across the windshield, a second motor for driving another of saidblades to and fro across the windshield, a plurality of conduitsinterconnecting the first and second motors so as to insure the.existence of substantially the same pressure conditions in the secondmotor as that prevailing in the first motor, a transmission including anexpansible link operatively connected to said blades, the phaserelationship of said blades being determined by whether or not said linkis being maintained in an expanded or contracted condition, and meansfor controlling the contracting and expanding of said link.

, it). A windshield cleaning system for automotive vehicles comprising,.a plurality of blades adapted to clear an associated windshield ofmoisture, a first motor for driving at least :one of said blades to andfro across the windshield, a second motor for driving another of saidblades to and fro across the windshield, a plurality of conduitsinterconnecting the first and second motors so as to insure theexistence of substantially the same pressure conditions in the second,motor as that prevailing in the first motor, a transmission including anexpansible pneumatic link operatively connected to said blades, thephase relationship of said blades being determined by whether or notsaid link is being maintained in an expanded or contracted condition, apneumatic system for expanding and contracting said link, and means forcontrolling the pn umatic system.

f 11. A windshield cleanin system for automotive vehiwindshield, asecond motor for driving another of said blades to and fro across thewindshield, the inboard ends of the operating'strokes of said bladesoverlapping one another, a transmission includingan expansible link;op.- eratively connected to said blades, the phaserelationship of saidblades being determined by whether or not said link is being maintainedin an expanded or contracted condition, and means for controllingthe'contracting and expanding of said link.

12. A windshield cleaning system for automotive vehicles comprising, aplurality of blades adapted to clear an associated windshield ofmoisture, a first motor for driving at least one of said blades to andfro across the windshield, a second motor for driving another of saidblades to and fro across the windshield, the inboard ends of theoperating strokes of said blades overlapping one another, a transmissionincluding an expansible pneumatic link opcratively connected to saidblades, the phase relationship of said blades being determined bywhether or not said link is being maintained in an expanded orcontracted condition, a pneumatic system for expanding and contractingsaid link, and means for controlling the pneumatic system.

13. A windshield cleaning system for automotive vehicles comprising, aplurality of blades adapted to clear an associated windshield ofmoisture, a first motor for driving at least one of said blades to andfro across the windshield, a second motor for driving another of saidblades to and fro across the windshield, a plurality of conduitsinterconnecting the first and second motors so as to insure theexistence of substantially the same pres.- sure con itio n he s con m ors t P va in in the first motor, a transmission including an expansihlelink operatively connected to said blades, the phase relationship ofsaid blades being determined by whether or not said link is beingmaintained in an expanded or cont acted condition, and control means,said last named means being adapted to simultaneously control theactivation and deactivation of the motors as well as the expansion andcontraction of the expansible link.

14. A windshield cleaning system for automotive vehicles compnising aplurality of blades adapted to clear an associated windshield ofmoisture, a first motor for driving at least one of said blades to andfro across the windshield, a second motor for driving another of saidblades to and fro across the windshield, a transmission including anexpansible pneumatic link operatively connected to said blades, thephase relationship of said blades, being determined by whether or notsaid link is being maintained in an expanded or contracted condition, aPneumatic system for expanding and contracting said link, and controlmeans, said last named means being adapted to simultaneously control theactivation and deactivation of the motors as well as the expansion andcontraction of the expansible link.

15. A windshield cleaning system for automotive yehicles compris g, aplurality of blades adapted to clear an associated windshield ofmoisture, a first motor for driving at least one of said blades to andfro across the windshield, a second motor for driving another of saidblades to and fro across the windshield, a plurality of conduitsinterconnecting the first and second motors so as to insure theexistence of substantially the same pressure conditions in the secondmotor as that prevailing in the first motor, the inboard ends of theoperating strokes of the blades overlapping one another, a transmissionincluding an expansible link operatively connected to said blades,..thephase relationship of said blades being, determined by whether or notsaid link is being maintained in .an expanded or contracted condition,control means, said last named means being adapted to 1 simultaneouslycontrol the activation ,and deactivation of the first and second motorsas well as the expansion and contraction of the expansible link.

16. A windshield cleaning system for automotive vehicles comprising, aplurality of blades adapted to clear contracted condition, a pneumaticsystem for expanding and contracting said link, and control means, saidlast named means being adapted to simultaneously control the activationand deactivation of the first and second an associated windshield ofmoisture, a first motor for 5 motors as well as the expansion andcontracting of the driving at least one of said blades to and fro acrossthe windshield, a second motor for driving another of said blades to andfro across the windshield, the inboard ends of the operating strokes ofsaid blades overlapping one another, a transmission including anexpansible pneumatic link operatively connected to said blades, thephase relationship of said blades being determined by whether or notsaid link is being maintained in an expanded or expansible link.

References Cited in the file of this patent UNITED STATES PATENTS2,263,053 Schuler Nov. 18, 1941 2,287,179 Kocher June 23, 1942 2,683,353OShei July 13, 1954

